Electric discharge lamp



Nov. 28, 1939. o H. BIGGS ELECTRIC DISCHARGE LAMP Filed Dec. 31, 1958rig.

' ORR/CK H. 5/665,

INVENTOR.

ATTORNEY.

Patented Nov. 28, 1.939

UNITED STATES PATENT OFFICE 2 cmm.. (or. 116-12 1) This inventionrelates to electric gaseous discharge lamps, and in particular toapparatus for properly operating such lamps.

An object of the invention is to provide for such a lamp a cathode whichis pre-heated'to facilitate starting of themain discharge, and apparatusto provide'the preheating'automatically for the proper period whenvoltage is applied to the lamp circuit.

Other objects and advantages of the invention will be apparent from thefollowing description taken in Connection with the accompanying drawingin which:

v Figure 1 is a schematic circuit diagram of apparatus embodying oneform of the invention;

Figure 2 is a schematic circuit diagram of apparatus embodying anotherform of the invention; and

Figure 3 is a view of the switching part of the circuit, after the lamphas started.

In Figure l. thegaseous electric discharge lamp l, comprises the sealedglass envelope 2, with an electrode'3 at each end of the tube, eachelectrode comprising a coil of wire, preferably tungsten, bearing anelectron-emissive coating, .such as a coating of the alkaline earthoxides. The tung sten coil is preferably of the coiled-coil ordoublycoiled type, in order to hold the oxide coating bet: ter, and toprovidea higher voltage drop across the cathode at starting, than woulda singly-coiled electrode. The use of such a coiled-coil electrode in adischarge lamp is recommended, for example, in United States Patent2,06l,892, issued November 24, 1936, to Laurence Burns.

Lead-in wires 4, 5, 6, I, extend from the ends of the coil through theends of the glass envelope 2, to act as contacts to the remainder of theapparatus. The tube contains a gaseous atmosphere. At one end of thetube, lead-in wire 8, is connected to one end of the power line fromwhich the lamp is operated; the power line may conveniently have avoltage of H0 volts. At the other endof the lamp, lead-in .4, isconnected to the other side of the power line through the reactance coil8. Lead-in wires 2 and 3 are normally connected together through thecontacts 9 and ill, but when the switch II, a double pole switch in thedrawing, is closed, allowing current to build up through the reactancecoil 8, the magnetic field of the coil pulls down the arm l2, which isof iron or other magnetic material, thus opening the circuit through thecontacts 9, I II.

For the period necessary for the current to build up through thereactance 8, the contacts 9, III, are closed, and current flows throughthe coils in the tube between the heated electrodes.

of electrodes 3, 3, bringing them to an electronemitting temperature.When the current builds up to the proper value, contacts 9, l0 open andthe current is then forced'to flow through the ggs T e current willordinarily build up too fast to allow time for properly preheating thecathodes unless a small cap i3 of copper or other conducting metal isplaced on the end of the magnetic pole N. This conducting patch slowsthe building up of however, or it will cause too great a power loss.

The arrangement of Figure 2 is the preferable form of the invention,because it allows a more careful adjustment and regulation of the periodof preheating the electrodes. In Figure 2, instead of depending on thedelay in magnetic fieldbuild-up' to allow time for the filaments to preheat before the contacts 9, III are opened, I depend on the action .of athermostatic switch,

which perinits 'a longer and more definitely con-.

trolled preheating period. The switch arm l6,

may be of phosphor bronze or other spring material, flexed to keep thecontacts 9, l0, normally closed. A bimetallic disc l8, that is, adisceach of whose sides is of a different metal, one for example being ofsteel and the other of bronze, is flexed downward as shown, beingsupported along its circumference, anda piece l5 of insulating materialis placed as shown between the disc and the switch arm. This piece isshort enough to allow the switch arm to remain closed when thebimetallic disc isflexed as shown, yet long enough to open the switchcontrols 9, it), if the disc is flexed upward. A small heating coil ll,in series with the circuit to the line, as shown, is placed near thebimetallic disc. When the switch II, is closed, current flows throughthe reactance coil 8, the filaments 3, 4 and the disc heater I'I.Current continues to flow until the heat from the heater I1, issufiicient to expand the metal on one side of the disc enough morethan'that on the other side, to cause the disc to temperature, say 700C., and then the thermo- 10, the magnetic field, because of the eddycurrents in the cap. The cap must not be made too large,

ment and connected to one which provides, because of the seriesreactance coil, a strong inductive voltage-kick across the gas between.the electrodes at each end of the tube, enabling the tube to start.

There is one 'further feature which facilitates starting of the lamp.The filament may be arranged, particularly if a coiled-coil filamentisused, to have a drop across it, prior to starting the lamp, somewhatabove the excitation or ionization potential of the gas used. In thatcase a small discharge may occur across the ends of the filament. Asmall wire, such as l9 or 20, in Figures 1 and 2 may be placed alongsidethe filaend-of the filament in which case the discharge may occurbetween thatwire and the portion of the filament which is above theionization voltage of the gas, with respect to the lead-in wires l or 8respectively.

The distance betweenwire and filament will be less than that between theends of the filament, and the filament, or auxiliary discharge, willmore easily pass.

We thus have the filament at the proper electron emitting temperature,the gas around the filament ionized, and an inductive voltage surgeacross the tube, all at the instant at which the bimetallic switchsnaps. The combination of all these factors produces'an effectivestarting arrangement for the lamp.

In the event that the lamp is too long to start from the 110-.volt lamp,a higher voltage may be used across the entire circuit, or a transformermay be used across the line. The transformer may be designed to havesufiicient leakage reactance to make the choke coil unnecessary inFigure 2, and may be deslgned to have the proper magnetic effect toreplace the choke in Figure 1 as well.

What I claim is: 1. In combination, a reactancecoil, a. heating coil, alamp filament of the oxide-coated coiledcoil tungsten wire type, anormally closed pair of contacts, and another lamp filament of the sametype as the first, all connected in series electrically, the lampfilaments being at opposite ends of a sealed glass envelope containing agaseous atmosphere, one of the contacts of said pair being.

snap to discharge the reactance coil through the lamp with a voltagesurge, the reactance coil having a reactance sufiicient to produce avoltage surge to start the discharge when the contacts snap open and tolimit the current to a value safe for the lamp while said contacts areopen, yet small enough to allow sumcient cv rent to flow through thefilament before the contacts are opened to produce a voltage drop acrosseach filament greater than the excitation voltage of the gas, and a wireconnected to one end of each filament and extending alongside andparallel to said filament toward the other end of said filament, toenable the passing of a small discharge between thewire and the end ofthe filament prior to the opening of the pair of contacts.

2. In combination, a lamp filament, a normally closed pair of contacts,and another lamp filament, all connected electrically in series, withthe pair of contacts between the two filaments and connecting one leadof one filament to one lead of the other filament, said filaments beingat opposite ends of a gaseous discharge lamp, a fiexed bimetallic discarranged to snap open the pair of contacts when said strip is heated fora sufilcient period, a heating coil for said bimetallic disc andelectrically connected in series with the lamp filaments so that thefiow of current through the lamp filament will begin the heating of thebimetallic disc, said disc being arranged with its heater so that itreaches its snapping temperature shortly after the filaments reach theirproper electron-emitting temperature, a reactance coil in series withsaid lamp filaments and having a reactance sufilcient to provide aninductive voltage surge between the electrodes at opposite ends of thetube when the contacts connecting the filaments snap open and sufficientto limit the current through the discharge to a value safe for the lampafter the discharge is started, yet small enough to provide, before saidcontacts are opened, a voltage drop across each filament, at itselectron-emitting temperature, greater than theexcitation voltage of thegas, and a wire close to and alongside each filament, said wire beingelectrically connected to one end of the filament and extending alongthe filament toward the other end of the filament and close enough tosaid other end of the filament to permit the passage of a smalldischarge between said wire and said filament at the voltage across thefilament prior to the opening of the pair of contacts, to insure thatthe gas around the filament is ionized at the instant the contacts open.

ORRICK H. BIGGS.

